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Two studies were conducted within the Prostate Cancer Prevention Trial in which prospective nutritional information was collected and all subjects were recommended to undergo biopsy. Findings included that, among 9,559 subjects there was no association between any supplement or nutrient (including fat) and risk of prostate cancer overall but the risk of high-grade cancer was associated with high intake of polyunsaturated fats. In a subset of 1,658 cases and 1,803 controls, specific fatty acids were examined and docosahexaenoic acid was associated with risk of high-grade disease while trans-fatty acids (TFA) 18:1 and TFA 18:2 were inversely associated with risk of high-grade disease. These large scale studies suggest a complex relationship between nutrients such as fat and risk of prostate cancer.[39,40]

The explanation for this possible association between prostate cancer and dietary fat is unknown. Several hypotheses have been advanced, including:

Dietary fat may increase serum androgen levels, thereby increasing prostate cancer risk. This hypothesis is supported by observations from South Africa and the United States that changes in dietary fat intake change urinary and serum levels of androgens.[41,42]

Certain types of fatty acids or their metabolites may initiate or promote prostate carcinoma development. The evidence for this hypothesis is conflicting, but one study suggests that linoleic acid (omega-6 polyunsaturated fatty acid) may stimulate prostate cancer cells, while omega-3 fatty acids inhibit cell growth.[43]

An observation made in an animal model is that male offspring of pregnant rats who are fed a high-fat diet will develop prostate cancer at a higher rate than animals who are fed a low-fat diet.[44] This observation may explain some of the variations in prostate cancer incidence and mortality among ethnic groups; an observation has been made that first trimester androgen levels in pregnant blacks are higher than those in whites.[45]

Dairy and Calcium Intake

In a meta-analysis of ten cohort studies (eight from the United States and two from Europe), it was concluded that men with the highest intake of dairy products (relative risk [RR] = 1.11; 95% confidence interval [CI], 1.00–1.22; P = .04) and calcium (RR = 1.39; 95% CI, 1.09–1.77; P = .18) were more likely to develop prostate cancer than men with the lowest intake. The pooled RRs of advanced prostate cancer were 1.33 (95% CI, 1.00–1.78; P = .055) for the highest versus lowest intake categories of dairy products and 1.46 (95% CI, 0.65–3.25; P > .2) for the highest versus lowest intake categories of calcium. High intake of dairy products and calcium may be associated with an increased risk of prostate cancer although the increase may be small.[46]